Do item bonuses act on base damage or altered damage?

If I have a +10 melee item and then get a +10% melee damage item, do they both only add to base melee or will the second one add 10% of the increased melee damage?

-edit- I thought of another question and I figured I'd just tag it on here rather than clutter up the sub with posts: For items that have an effect "on spell damage", what counts as spell damage? Does a spell that buffs to add lightenting damage to the next melee (like Thunderstrike) count as spell damage, or does spell damage need to be direct, immediate damage?